This Program Project will investigate basic regulatory mechanisms of colonic motility. Experiments will investigate the cellular and molecular basis for spontaneous electrical rhythmicity in colonic muscles and these cells respond to neural inputs. The first project will investigate the physiological role of interstitial cells of Cajal. These cells are thought to be pacemaker cells in the gastrointestinal (GI) tract and to have an important role in neurotransmission. The development and plasticity of ICC will be investigated because recent evidence has suggested that loss of ICC could be a factor in a variety of motility disorders. The second project will study the molecular biology of ionic conductances expressed by smooth muscle cells and ICC. Ionic conductances will be cloned and expressed by smooth muscle cells and ICC. Ionic conductances will be cloned and expressed in heterologous expression systems to study the properties and regulation of the ionic conductances responsible for generating GI motility and responses to enteric neurons. The third project will compliment the finds of the second project by studying the ionic conductances of native smooth muscle cells that are responsible for setting membrane potential and regulating excitability. Several novel ionic conductances will be evaluated and characterized by these projects. The fourth project will study the cellular basis for neural regulation of GI motility. Ionic conductances in identify populations of enteric neurons. Whole cell imaging of Ca2+ transients in enteric neurons in situ will be correlated with the electrical behavior of neurons and regulation of the open probabilities of Ca2+-dependent conductances. The fifth project will investigate the role of non-receptor tyrosine kinases in coupling neurotransmitter receptors to ionic conductances, Ca2+ transients and mechanical events in smooth muscle cells. These projects will be supported by an administrative core and two core laboratory facilities. The tissue culture core will manage the mouse colony, provide tissues and oocytes, prepare isolated cells, and culture interstitial cells and strips of muscle. The molecular/morphology core will provide morphological support by preparing tissues and performing immunohistochemistry, in situ hybridization, and electron microscopy. This core will also provide molecular services such as preparing molecular reagents and performing tests to determine expression of specific genes in smooth muscle cells, neurons and ICC. Together the Projects and Cores will conduct a rigorous, highly focused investigation of the cellular mechanisms that regulate smooth muscle. The results will continue to expand our understanding of GI motility and provide a basis for the development of new treatments and therapeutic agents for motility disorders.